P3ht:Pcbm Polymer Solar Cells from a Didactic Perspective

Abstract

In this work, we studied the influence of pre- and post thermal annealing on the performance of polymer:fullerene bulk heterojunction (BHJ) solar cells using the conventional architecture, comprising a conjugated polymer, namely, poly(3-hexylthiophene-2,5-diyl) (P3HT) and a fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester (PC 60 BM) as a photoactive layer. The non-annealed active layer device exhibited a power conversion efficiency of less than 1%, which was significantly lower than the pre- and post-annealed devices. In order to investigate the impact of pre- and post thermal annealing on the natural morphological state of the polymer, regiorandom (P3HT-I) and regioregular (P3HT-II) type P3HT were compared in photoactive layers. In general, P3HT-I is amorphous, whereas P3HT-II is semi-crystalline. Changes in solar cell performance were associated with changes in carrier extraction efficiencies influenced by the annealing conditions. The charge photogeneration processes were investigated using spectroscopic techniques, including electroluminescence (EL), steady-state, and time-resolved photoluminescence (TR-PL) spectroscopy. Finally, to explore the morphological changes upon annealing, atomic force microscopy (AFM) and electroluminescence imaging (ELI) measurements were performed on films and solar cells, respectively.

Keywords: Bulk-heterojunction polymer solar cells, P3HT:PCBM solar cells, thermal annealing, pre-and post-annealing.